This project studies electrophysiological correlates of cognitive dysfunction in obsessive- compulsive disorder (OCD). Abnormalities of event-related brain potentials (ERPs) in OCD, in particular enhanced N200 and attention- related processing negativity (Nd), are consistent with a hypothesis of overaroused and overfocused attention to OCD. The investigator proposes to further evaluate this hypothesis and explore regional hemispheric differences in OCD patients by measuring ERPs during auditory tasks with varying cognitive demands and by using an expanded array of scalp electrodes. Examination of clinical and neurological correlates of ERP abnormalities in OCD will also continue to evaluate the hypothesis that OCD is a "heterogeneous diagnostic syndrome."A long range goal of this research is to help identify OCD subtypes with distinctive pathophysiology and clinical features, i.e., symptom severity and outcome of treatment. ERP components (N200, Nd, P300) and behavioral responses of 80 OCD patients, 30 patient controls with other anxiety disorders (social phobia or panic disorders), and 30 normal controls will be measured during binaural oddball tasks, directed attention tasks, and dichotic listening tasks. A verbal (nonsense syllable) and nonverbal (complex tone) version of each task will be used to further evaluate hypotheses concerning left hemisphere overactivation and dysfunction in OCD. Resting EEG alpha power will also be measured to provide an index of cortical arousal. All patients will be tested after a 2 week drug-free period, and a minimum of 30 OCD patients will be retested following 12 weeks of treatment with an antiobsessional medication (clomipramine) and/or behavior therapy. This will determine whether or not ERP abnormalities in OCD are normalized following clinical improvement.